Design and energy, exergy, thermoeconomic, and exergo-environmental (4E) analyses of a novel hybrid geothermal/biogas-powered green multi-generation system using a post-combustion CO2 capture unit

This research introduces a novel multigeneration method that enables the simultaneous generation of electrical power, fresh water, hydrogen, hot water, and cold water. The energy required for this process is derived from geothermal fluid and biogas. A post-combustion mechanism is used in this novel method to separate carbon dioxide and reduce emissions. In addition, the heat produced by burning biogas is used in an organic Rankine cycle to generate power, which is thermally integrated with a Kalina cycle. The waste heat generated by the Kalina cycle is applied to produce hot water and facilitate fluid evaporation in the vapor generator of the absorption chiller cycle. Hydrogen is generated in a PEM electrolyzer, where the necessary electricity is provided directly within the system. A exergy analysis was performed to determine the system's irreversibility and pinpoint the area with the greatest exergy destruction. The findings revealed that the overall exergy destruction of this system is 17,412 kW, with the combustion reactor being the primary contributor, responsible for 63.2 % of the irreversibility. Furthermore, the study revealed that the evaporator in the absorption chiller cycle has the greatest value for the parameter known as the “ environmental damage effectiveness factor.” To tackle this problem, a remedy was suggested during the sensitivity analysis. The sensitivity analysis demonstrated that raising the feed temperature of the stripper column in the post-combustion section can improve both energy and exergy efficiency, without any impact on the production rate. The modeling results obtained using Aspen HYSYS indicate that the suggested process has exergy efficiency, electrical efficiency and energy efficiency and values of 23.67 %, 16.38 % and 51.15 %, respectively. In addition, the thermoeconomic evaluation demonstrated that the annual cost of this new process amounts to 11,255,260 $. Taking into account the production rate of the system, the key parameter levelized cost of energy was calculated to be 0.1172 $/kWh. An analysis of different parameters showed that raising the temperature of the feed in the stripper column to 118 °C can result in a decrease in the levelized cost of energy by $0.085/kWh due to a reduction in geothermal energy consumption. Additionally, this modification resulted in an enhancement of the energy efficiency and exergy efficiency to 77 % and 26 %, respectively.